Mine loves the beach too but is OBSESSED with big rocks...
as soon as you get to the beach no ball will do.... just big rocks that you have to throw a few feet into the sea then she drags it out and repeats
Have to put her on lead an physically drag her away as she cries cos she doesn't want to leave the rock behind lol
my parents old dog when i was a kid used to love rocks. wore all his teeth down to practically stumps through chewing on them.